Semiconductor element coating glass and semiconductor element coating material using same

ABSTRACT

Provided is a glass for semiconductor device coating, which is substantially free of an environmental load substance, is excellent in acid resistance, and has a low surface charge density while enabling coating at a firing temperature of 900° C. or less. The glass for semiconductor device coating of the present invention includes, as a glass composition, 40% to 65% of ZnO+SiO2, 7% to 25% of B2O3, 5% to 15% of Al2O3, and 8% to 22% of MgO, and is substantially free of a lead component.

TECHNICAL FIELD

The present invention relates to a glass for semiconductor devicecoating and a material for semiconductor coating using the glass forsemiconductor device coating.

BACKGROUND ART

In a semiconductor device, such as a silicon diode or a transistor, ingeneral, a surface including a P-N junction of the semiconductor deviceis coated with a glass. With this configuration, stabilization of thesurface of the semiconductor device can be achieved, and deteriorationof the characteristics with time can be suppressed.

Examples of the characteristics required for the glass for semiconductordevice coating include the following: (1) the glass for semiconductordevice coating has a thermal expansion coefficient compatible with athermal expansion coefficient of the semiconductor device so that acrack or the like due to a difference in thermal expansion coefficientwith the semiconductor device may not occur; (2) coating can beperformed at low temperature (e.g., 900° C. or less) to preventdeterioration of the characteristics of the semiconductor device; (3)the glass for semiconductor device coating has such acid resistance asto be free from being eroded in an acid treatment step performed after acoating layer is formed; and (4) a surface charge density is regulatedin a certain range in order to optimize electrical characteristics ofthe semiconductor device.

A lead-based glass, such as a PbO—SiO₂—Al₂O₃—B₂O₃-based glass, hasheretofore been known as the glass for semiconductor device coating (forexample, Patent Literature 1), but from the viewpoint of avoidingcontaining an environmental load substance, a zinc-based glass, such asa ZnO—B₂O₃—SiO₂-based glass, is currently in the mainstream (see, forexample, Patent Literature 2).

CITATION LIST

-   Patent Literature 1: JP 11-236239 A-   Patent Literature 2: WO 2014/155739 A1

SUMMARY OF INVENTION Technical Problem

However, there is a problem in that the zinc-based glass is inferior inchemical durability as compared to the lead-based glass, and hence isliable to be eroded in an acid treatment step performed after a coatinglayer is formed. Accordingly, a protective film needs to be furtherformed on a surface of the coating layer before performing the acidtreatment.

In order to solve the above-mentioned problem, when the content of SiO₂in a glass composition becomes larger, a reverse voltage of asemiconductor device is improved as well as acid resistance is improved,but there is a failure that a reverse leakage current of thesemiconductor device is increased. In particular, in a semiconductordevice for low withstand voltage, it is given a higher priority tosuppress the reverse leakage current to reduce a surface charge densitythan to improve the reverse voltage, and hence the above-mentionedproblem becomes apparent. In addition, a softening point of the glasssignificantly increases, and hence when coating is performed bylow-temperature firing (e.g., 900° C. or less), softening flowability ofthe glass is impaired. Accordingly, it becomes difficult to uniformlycoat the surface of the semiconductor device.

Accordingly, the present invention has been made in view of theabove-mentioned circumstances, and a technical object of the presentinvention is to provide a glass for semiconductor device coating, whichis substantially free of an environmental load substance, is excellentin acid resistance, and has a low surface charge density while enablingcoating at a firing temperature of 900° C. or less.

Solution to Problem

The inventor of the present invention has made extensive investigations,and as a result, has found that the above-mentioned technical object canbe achieved by using a glass having a specific composition. Thus, thefinding is proposed as the present invention. That is, according to oneembodiment of the present invention, there is provided a glass forsemiconductor device coating, comprising as a glass composition, interms of mol %, 40% to 65% of ZnO+SiO₂, 7% to 25% of B₂O₃, 5% to 15% ofAl₂O₃, and 8% to 22% of MgO, and being substantially free of a leadcomponent. Herein, the “ZnO+SiO₂” represents the total of the contentsof ZnO and SiO₂. In addition, the “substantially free of” means that theexplicit component is not intentionally added as a glass component, andthe case in which even impurities that are inevitably mixed arecompletely excluded is not meant. Specifically, the case in which thecontent of the explicit component including impurities is less than 0.1mass % is meant.

As described above, in the glass for semiconductor device coatingaccording to the one embodiment of the present invention, the contentrange of each component is regulated. With this configuration, the glassfor semiconductor device coating is substantially free of anenvironmental load substance, is excellent in acid resistance, and has areduced surface charge density while enabling coating at a firingtemperature of 900° C. or less. As a result, the glass for semiconductordevice coating can be suitably used for coating a semiconductor devicefor low withstand voltage.

Further, the glass for semiconductor device coating according to the oneembodiment of the present invention preferably has a molar ratioSiO₂/ZnO in the glass composition of from 0.5 to 2.0. With thisconfiguration, improvement in acid resistance and coating at a firingtemperature of 900° C. or less can both be achieved.

Further, the glass for semiconductor device coating according to the oneembodiment of the present invention preferably has a molar ratioAl₂O₃/(ZnO+SiO₂) in the glass composition of from 0.08 to 0.30. Withthis configuration, meltability of the glass can be maintained whilestability and acid resistance of the glass are maintained.

The glass for semiconductor device coating according to the oneembodiment of the present invention preferably has a thermal expansioncoefficient within the temperature range of from 30° C. to 300° C. offrom 20×10⁻⁷/° C. to 55×10⁻⁷/° C. Herein, the “thermal expansioncoefficient within the temperature range of from 30° C. to 300° C.”refers to a value measured with a push-rod-type thermal expansioncoefficient measurement apparatus.

According to another embodiment of the present invention, there isprovided a material for semiconductor device coating, preferablycomprising 75 mass % to 100 mass % of glass powder formed of theabove-mentioned glass for semiconductor device coating and 0 mass % to25 mass % of ceramic powder.

The material for semiconductor device coating according to the otherembodiment of the present invention preferably has a thermal expansioncoefficient within the temperature range of from 30° C. to 300° C. offrom 20×10⁻⁷/° C. to 55×10⁻⁷/° C.

DESCRIPTION OF EMBODIMENTS

A glass for semiconductor device coating of the present invention ischaracterized by comprising as a glass composition, in terms of mol %,40% to 65% of ZnO+SiO₂, 7% to 25% of B₂O₃, 5% to 15% of Al₂O₃, and 8% to22% of MgO, and being substantially free of a lead component.

The reasons for limiting the content of each component are describedbelow. The expression “%” means “mol %” in the following description ofthe content of each component unless otherwise stated.

ZnO+SiO₂ is a component that stabilizes the glass. The content ofZnO+SiO₂ is from 40% to 65%, preferably from 43% to 63%, more preferablyfrom 45% to 60%, still more preferably from 47% to 58%, particularlypreferably from 50% to 55%. When the content of ZnO+SiO₂ becomes lessthan 40%, vitrification at the time of melting becomes difficult, and inaddition, even when the vitrification occurs, devitrification(unintended crystal) precipitates from the glass at the time of firing,and softening and flowing of the glass are inhibited, and hence itbecomes difficult to uniformly coat the surface of the semiconductordevice. Meanwhile, when the content of ZnO+SiO₂ exceeds 65%, thesoftening point of the glass significantly increases, and the softeningand flowing of the glass at 900° C. or less are inhibited, and hence itbecomes difficult to uniformly coat the surface of the semiconductordevice.

ZnO is a component that stabilizes the glass. The content of ZnO ispreferably from 10% to 40%, more preferably from 15% to 38%, still morepreferably from 20% to 351, particularly preferably from 25% to 32%.When the content of ZnO is too small, a devitrification property at thetime of melting becomes strong, and hence it becomes difficult to obtainhomogeneous glass. Meanwhile, when the content of ZnO is too large, acidresistance is liable to be reduced.

SiO₂ is a network-forming component of the glass, and hence is acomponent that stabilizes the glass and enhances the acid resistance.The content of SiO₂ is preferably from 15% to 45%, more preferably from18% to 42%, still more preferably from 20% to 38%, particularlypreferably from 25% to 35%. When the content of SiO₂ is too small, thereis a tendency that the acid resistance is reduced. Meanwhile, when thecontent of SiO₂ is too large, the softening point of the glasssignificantly increases, and the softening and flowing of the glass at900° C. or less are inhibited, and hence it becomes difficult touniformly coat the surface of the semiconductor device.

B₂O₃ is a network-forming component of the glass, and is also acomponent that enhances softening flowability. The content of B₂O₃ isfrom 7% to 25%, preferably from 10% to 22%, more preferably from 12% to18%. When the content of B₂O₃ is too small, crystallinity becomes high,and softening flowability of the glass is impaired at the time ofcoating, and hence it becomes difficult to uniformly coat the surface ofthe semiconductor device. Meanwhile, when the content of B₂O₃ is toolarge, there are tendencies that a thermal expansion coefficient isimproperly increased and the acid resistance is reduced.

Al₂O₃ is a component that improves the acid resistance and adjusts asurface charge density. The content of Al₂O₃ is from 5% to 15%,preferably from 7% to 14%, more preferably from 9% to 13%, particularlypreferably from 10% to 12%. When the content of Al₂O₃ is too small, theglass becomes liable to devitrify, and the acid resistance is reduced.Meanwhile, when the content of Al₂O₃ is too large, there is a risk inthat the surface charge density may become too large, and there is alsoa risk in that a crystal may precipitate from a glass melt at the timeof melting and melting may become difficult.

MgO is a component that reduces the viscosity of the glass. The contentof MgO is from 8% to 22%, preferably from 9% to 20%, more preferablyfrom 10% to 19%, still more preferably from 11% to 18%, particularlypreferably from 12% to 17%. when the content of MgO is too small, thefiring temperature of the glass is liable to increase. Meanwhile, whenthe content of MgO is too large, there are risks in that the thermalexpansion coefficient may become too high, the acid resistance may bereduced, and an insulating property may be reduced.

In order to achieve both of improvement in acid resistance and coatingat a firing temperature of 900° C. or less, the molar ratio SiO₂/ZnO inthe glass composition is preferably from 0.5 to 2.0, from 0.6 to 1.8, orfrom 0.8 to 1.6, particularly preferably from 1.0 to 1.4. When the molarratio SiO₂/ZnO is too small, the acid resistance is reduced. Meanwhile,when the molar ratio SiO₂/ZnO is too large, the softening point of theglass is significantly increased, the softening and flowing of the glassat 900° C. or less are inhibited, and hence it becomes difficult touniformly coat the surface of the semiconductor device.

When the balance of Al₂O₃, ZnO, and SiO₂ in the glass composition istaken into consideration, poor meltability can be avoided while thestability and the acid resistance of the glass are maintained. The molarratio Al₂O₃/(ZnO+SiO₂) in the glass composition is preferably from 0.08to 0.30, more preferably from 0.10 to 0.25, still more preferably from0.12 to 0.20, particularly preferably from 0.14 to 0.18. When the molarratio Al₂O₃/(ZnO+SiO₂) is too small, the melting of the glass is liableto become difficult. Meanwhile, when the molar ratio Al₂O₃/(ZnO+SiO₂) istoo large, the stability and the acid resistance of the glass are liableto be reduced.

In addition to the above-mentioned components, the glass may containanother component (e.g., CaO, SrO, BaO, MnO₂, Ta₂O₅, Nb₂O₅, CeO₂, orSb₂O₃) at up to 7% (preferably up to 3%).

From the environmental viewpoint, it is preferred that the glass besubstantially free of a lead component (e.g., PbO) and be alsosubstantially free of Bi₂O₃, F, or Cl. In addition, it is preferred thatthe glass be also substantially free of alkali components (Li₂O, Na₂O,and K₂O) that have an adverse influence on the surface of thesemiconductor device.

The glass for semiconductor device coating of the present invention ispreferably a powder form, that is, glass powder. When the glass forsemiconductor device coating is processed into glass powder, the surfaceof the semiconductor device can be easily coated using, for example, apaste method or an electrophoretic coating method.

The glass powder has an average particle diameter D₅₀ of preferably 25μm or less, particularly preferably 15 μm or less. When the averageparticle diameter D₅₀ of the glass powder is too large, pasting becomesdifficult. In addition, powder adhesion by an electrophoretic methodalso becomes difficult. The lower limit of the average particle diameterD₅₀ of the glass powder is not particularly limited, but isrealistically 0.1 μm or more. The “average particle diameter D₅₀” refersto a value measured on a volume basis and a value measured by a laserdiffraction method.

The glass for semiconductor device coating of the present invention maybe obtained by, for example, blending raw material powders of therespective oxide components to form a batch, melting the batch to causevitrification at about 1,500° C. for about 1 hour, and then forming (andthen pulverizing and classifying as required) the resultant.

A material for semiconductor device coating of the present inventioncontains the glass powder formed of the glass for semiconductor devicecoating, and may also be mixed with ceramic powder as required to formcomposite powder. When the ceramic powder is added, the thermalexpansion coefficient can be easily adjusted.

As the ceramic powder, powders formed of zirconium phosphate, zircon,zirconia, tin oxide, aluminum titanate, quartz, β-spodumene, mullite,titania, quartz glass, β-eucryptite, β-quartz, willemite, cordierite,and the like may be used alone or as a mixture thereof.

The mixing ratio of the glass powder and the ceramic powder is asfollows: preferably 75 vol % to 100 vol % of the glass powder and 0 vol% to 25 vol % of the ceramic powder; more preferably 80 vol % to 99 vol% of the glass powder and 1 vol % to 20 vol % of the ceramic powder;still more preferably 85 vol % to 95 vol % of the glass powder and 5 vol% to 15 vol % of the ceramic powder. When the content of the ceramicpowder is too large, the ratio of the glass powder becomes relativelysmall, and softening and flowing of the glass are inhibited, and henceit becomes difficult to coat the surface of the semiconductor device.

The ceramic powder has an average particle diameter D₅₀ of preferably 30μm or less, particularly preferably 20 μm or less. When the averageparticle diameter D₅₀ of the ceramic powder is too large, smoothness ofthe surface of a coating layer is liable to be reduced. The lower limitof the average particle diameter D₅₀ of the ceramic powder is notparticularly limited, but is realistically 0.1 μm or more.

The material for semiconductor device coating of the present inventionhas a thermal expansion coefficient within the temperature range of from30° C. to 300° C. of preferably from 20×10⁻⁷/° C. to 55×10⁻⁷/° C., morepreferably from 30×10⁻⁷/° C. to 50×10⁻⁷/° C. When the thermal expansioncoefficient falls outside of the above-mentioned ranges, a crack,warpage, or the like due to a difference in thermal expansioncoefficient with the semiconductor device is liable to occur.

When, for example, the surface of the semiconductor device of 1,000 V orless is to be coated, the material for semiconductor device coating ofthe present invention has a surface charge density of preferably12×10¹¹/cm² or less, more preferably 10×10¹¹/cm² or less. When thesurface charge density is too high, withstand voltage becomes high, butat the same time, there is a tendency that a leakage current alsoincreases. The “surface charge density” refers to a value measured by amethod described in the “Examples” section to be described below.

Examples

Now, the present invention is described in detail by way of Examples.The following Examples are merely illustrative. The present invention isby no means limited to the following Examples.

Examples (Sample Nos. 1 to 4) and Comparative Examples (Sample Nos. 5 to8) of the present invention are shown in Table 1.

TABLE 1 No. No. No. No. No. No. No. No. 1 2 3 4 5 6 7 8 Glass ZnO 27 3030 17 28 18 35 25 composition SiO₂ 30 28 24 32 10 40 32 22 (mol %) B₂O₃16 15 17 20 25 16 7 26 Al₂O₃ 10 10 11 12 15 17 18 14 MgO 17 17 18 19 229 8 13 ZnO + SiO₂ 57 58 54 49 38 58 67 47 SiO₂/ZnO 1.11 0.93 0.80 1.880.36 2.22 0.91 0.88 Al₂O₃/(ZnO + SiO₂) 0.18 0.17 0.20 0.24 0.39 0.290.27 0.30 Glass powder 100 100 100 85 100 100 100 100 (mass %) Ceramicpowder 0 0 0 Cordierite 15 0 0 0 0 (mass %) Thermal expansion 44 45 4631 No 35 43 45 coefficient vitrification (×10⁻⁷/° C.) Surface charge 4 63 7 18 >20 11 density (×10¹¹/cm²) Coating property ∘ ∘ ∘ ∘ x x ∘ Acidresistance ∘ ∘ ∘ ∘ ∘ ∘ x

Each sample was produced as described below. First, raw material powderswere blended so as to have a glass composition of Table 1 to form abatch, and the batch was melted to vitrify at 1,500° C. for 2 hours.Subsequently, the molten glass was formed into a film shape, and thenpulverized with a ball mill and classified with a 350-mesh sieve toprovide glass powder having an average particle diameter D₅₀ of 12 μm.In Sample No. 4, 15 mass % of cordierite powder (average particlediameter D₅₀: 12 μm) was added to the obtained glass powder to formcomposite powder.

For each sample, the thermal expansion coefficient, the surface chargedensity, the coating property, and the acid resistance were evaluated.The results are shown in Table 1.

The thermal expansion coefficient is a value measured using apush-rod-type thermal expansion coefficient measurement apparatus withinthe temperature range of from 30° C. to 300° C.

The surface charge density was measured as described below. First, eachsample was dispersed into an organic solvent and was caused to adhereonto a surface of a silicon substrate by electrophoresis so as to have aconstant film thickness. The resultant was then fired to form a coatinglayer. Next, an aluminum electrode was formed on a surface of thecoating layer, and then a change in electric capacity in the coatinglayer was measured with a C-V meter, and the surface charge density wascalculated.

The coating property was evaluated as described below. Each sample wascollected so as to have a weight of its density, and the resultant wasplaced into a die having a diameter of 20 mm, and was subjected to pressmolding to produce a dry button. The dry button was then placed onto aglass substrate, and was fired (retention time: 10 minutes) at 900° C.,and the flowability of the fired body was observed. A fired body havinga flow diameter of 18 mm or more was judged to be “o”, and a fired bodyhaving a flow diameter of less than 18 mm was judged to be “x”.

The acid resistance was evaluated as described below. Each sample wassubjected to press molding to have a diameter of 20 mm and a thicknessof about 4 mm, and was then fired (retention time: 10 minutes) at 900°C. to produce a pellet-shaped sample. A change in mass per unit area wascalculated from a loss of the mass of the sample after having beenimmersed in 30% nitric acid at 25° C. for 1 minute. The result was usedas an indicator of the acid resistance. A change in mass per unit areaof less than 1.0 mg/cm² was judged to be “o”, and a change in mass perunit area of 1.0 mg/cm² or more was judged to be “x”.

As apparent from Table 1, Sample Nos. 1 to 4 each had a surface chargedensity of 12×10¹¹/cm² or less, and received satisfactory evaluation forthe coating property and the acid resistance. Accordingly, Sample Nos. 1to 4 may each be suitable as a material for semiconductor device coatingto be used for coating the semiconductor device for low withstandvoltage.

Meanwhile, no vitrification occurred in Sample No. 5 because the contentof ZnO+SiO₂ was small. Sample No. 6 had a large content of Al₂O₃, andhence the surface charge density was increased and poor. In addition,Sample No. 7 had a large content of ZnO+SiO₂, and hence had poor coatingproperty. In addition, the content of Al₂O₃ was large, and hence thesurface charge density thereof was increased and poor. Further, SampleNo. 8 had a large content of B₂O₃, and hence had poor acid resistance.

1. A glass for semiconductor device coating, comprising as a glasscomposition, in terms of mol %, 40% to 65% of ZnO+SiO₂, 7% to 25% ofB₂O₃, 5% to 15% of Al₂O₃, and 8% to 22% of MgO, and being substantiallyfree of a lead component.
 2. The glass for semiconductor device coatingaccording to claim 1, wherein the glass for semiconductor device coatinghas a molar ratio SiO₂/ZnO of from 0.5 to 2.0.
 3. The glass forsemiconductor device coating according to claim 1, wherein the glass forsemiconductor device coating has a molar ratio Al₂O₃/(ZnO+SiO₂) of from0.08 to 0.30.
 4. The glass for semiconductor device coating according toclaim 1, wherein the glass for semiconductor device coating has athermal expansion coefficient within a temperature range of from 30° C.to 300° C. of from 20×10⁻⁷/° C. to 55×10⁻⁷/° C.
 5. A material forsemiconductor device coating, comprising: 75 mass % to 100 mass % ofglass powder formed of the glass for semiconductor device coating ofclaim 1; and 0 mass % to 25 mass % of ceramic powder.
 6. The materialfor semiconductor device coating according to claim 5, wherein thematerial for semiconductor device coating has a thermal expansioncoefficient within a temperature range of from 30° C. to 300° C. of from20×10⁻⁷/° C. to 55×10⁻⁷/° C.